1. Technical Field
The present invention relates to a length measuring device for measuring the position of two objects that are displaceable relative to one another. To protect the scale, the scale is disposed inside a hollow profile of the length measuring device, extending in the measuring direction. Such a length measuring device serves to measure lengths, travel paths, and positions, and is employed especially in machining equipment for measuring the relative motion of a tool with respect to a workpiece that is to be machined, in coordinate measuring machines, and increasingly in the semiconductor industry as well.
2. Background Information
Often, it is necessary that the length measuring device be embodied for measuring especially long travel paths over several meters. One such length measuring device is described for instance in German patent disclosure DE 43 18 017 A1. The length measuring device there includes a plurality of parts in the form of hollow profiles disposed in succession in the measuring direction. A scale in the form of a measuring tape extends in a groove in the hollow profiles over all the hollow profiles and is clamped via a fastening element inside the measurement range to one of the hollow profiles. That hollow profile is in turn fixed by screws in stationary fashion on the object to be measured.
A disadvantage of this is that the seals on the ends must, on the one hand, securely seal the hollow profiles from one another and, on the other hand, they must enable mechanical uncoupling. The seals are therefore the cause of relatively major contrary forces on the fastening element, which adversely affects the measurement accuracy.